如何在 C 中读取和覆盖文本文件？

Question

我有一个文本文件 text.txt 读取（为简单起见）

this is line one
this is line two
this is line three

再次为简单起见，我只是想将每行中的第一个字符设置为“x”，所以我想要的结果是

xhis is line one
xhis is line two
xhis is line three

所以我打开 text.txt 文件并尝试用所需的输出覆盖每一行到同一个文本文件。在 while 循环中，我将每行中的第一个字符设置为“x”。我还将变量“line”设置为等于一，因为如果它在第一行，我想倒退到文件的开头，以便在文件的开头而不是结尾覆盖。然后行增加，因此它将跳过下一次迭代的倒带，并应继续覆盖第 2 和第 3 行。它非常适合第一行。

有人有解决办法吗？顺便说一句，我在 stackoverflow 和其他网站上对此进行了广泛的研究，但没有运气。这是我的代码，我的输出也在下面：

#include <stdio.h>
#include <stdlib.h>
#define MAX 500

int main() {
    char *buffer = malloc(sizeof(char) * MAX);
    FILE *fp = fopen("text.txt", "r+");
    int line = 1;
    while (fgets(buffer, 500, fp) != NULL) {
            buffer[0] = 'x';
            if (line == 1) {
                    rewind(fp);
                    fprintf(fp, "%s", buffer);
            }
            else {
                    fprintf(fp, "%s", buffer);
            }
            line++;
    }
    free(buffer);
    fclose(fp);
}

输出：

xhis is line one
this is line two
xhis is line two
e
x

Answer 1

long pos = ftell(fp);//Save the current position
while (fgets(buffer, 500, fp) != NULL) {
    buffer[0] = 'x';
    fseek(fp, pos, SEEK_SET);//move to beginning of line
    fprintf(fp, "%s", buffer);
    fflush(fp);
    pos = ftell(fp);//Save the current position
}

Answer 2

我总是建议使用另一个文件来做这种解决方案。

1. 阅读该行
2. 将 x 放入新文件的一行中，然后复制该行的其余部分。
3. 这样做直到你得到 EOF
4. 删除旧文件
5. 重命名这个新文件

Answer 3

试试这个

#include<stdio.h>
#include<stdio.h>
#include<string.h>
int main()
{
    char buffer[500],read[50][50];
    FILE *fp=fopen("text.txt","r+");
    int line =1;
    while(fgets(buffer,500,fp)!=NULL){
        buffer[0]='x';
        printf("\n%d ",line);
        puts(buffer);
        strcat(read[line-1],(const char*)buffer);
        line++;
    }
    fclose(fp);
    FILE *fp1=fopen("text.txt","w");
    rewind(fp1);
    fprintf(fp1,"%s",read);
    return 0;
    }

我在windows上解决了这个问题

Answer 4

// file_overwrite.cpp : main project file.
// File opens and write y value to a file
// again reads same file and re-writes y value to a file

#include "stdafx.h"

using namespace System;

#include<stdio.h>
#include<stdio.h>
#include<string.h>
#include <conio.h>
#include<stdlib.h>

int main(int argc, char *argv[])
{
    int x = 19530;

    FILE *fp1 = fopen("D:\\Data\\BUFF.txt","w+");

    if(fp1 == NULL)
        printf("File not opening \n");
        int y=x;
        fprintf(fp1, "%d \n", y);
        fclose(fp1);
        printf("\n file -> open -> write y value and close");


        freopen("D:\\Data\\BUFF.txt", "w", fp1);
        rewind(fp1);
        y=100;
        fprintf(fp1, "%d \n", y);
        printf("\n file -> Reopen -> rewind write y values and close");
        fclose(fp1);

       getch();
       return 0;
}

Answer 5

// overwrite_file.cpp 
// File opens and write y value to a file
// again reads same file and re-writes y value to a file

#include "stdafx.h"

using namespace System;

#include<stdio.h>
#include<stdio.h>
#include<string.h>                //Include appropriate headers
#include <conio.h>
#include<stdlib.h>

int main(int argc, char *argv[])
{
    int x = 19530;                            // Give any value in the limit

    FILE *fp1 = fopen("D:\\Data\\BUFF.txt","w+");   // open file to write

    if(fp1 == NULL)                                 // if the file pointer encounters a null, it may not open neither overwrite 
        printf("File not opening \n");
        int y=x;                                     
        fprintf(fp1, "%d \n", y);                   //print y
        fclose(fp1);
        printf("\n file -> open -> write y value and close");  // close the file after writing the value of y


        freopen("D:\\Data\\BUFF.txt", "w", fp1);            //reopen and rewind file 
        rewind(fp1);
        y=100;                                              // this value of y given within the limits gets printed on the .exe console
        fprintf(fp1, "%d \n", y);
        printf("\n file -> Reopen -> rewind write y values and close");    // rewind write values and close 
        fclose(fp1);

       getch();
       return 0;
}